Coaxial structures such as cables and hermetic R.F. connectors include inner and outer cylindrical conductors separated by a dielectric medium, typically of glass. It has been difficult to achieve optimum electrical performance of these devices because of lack of uniformity in the meniscus of the glass-to-metal seals which terminate the connectors, and also lack of parallelism of the glass end surfaces. Since glass has a relatively high dielectric constant (.epsilon..sub.r =5), small physical variations can lead to large variations in electrical performance.
In the prior art it is known to utilize polymeric materials such as teflon or polyethylene as the dielectric material. However, large differences in the coefficient of thermal expansion between these polymers and the surrounding metal make it impossible to obtain a hermetic seal.
It would therefore be desirable to have a low dielectric constant material for use in coaxial structures, particularly in sub-miniature type-A (S.M.A) R.F. connectors so that design tolerances could be relaxed and R.F. performance and ease of manufacturability be increased. These improvements should be accomplished without sacrificing hermiticity or mechanical strength.